The present invention relates to a method of and an apparatus for correcting an image signal produced by scanning a stimulable phosphor sheet on which radiation image information is recorded, with a stimulating light beam to cause the stimulable phosphor sheet to emit light representative of the recorded radiation image information, and photoelectrically detecting the emitted light, and more particularly to a method of and an apparatus for correcting a change in an image signal due to a variation in the scanning speed at which the stimulable phosphor sheet is scanned with the stimulating light beam, by detecting such a variation in the scanning speed.
There has recently been known a radiation image information recording and reproducing system for producing the radiation-transmitted image of an object using a stimulable phosphor material capable of emitting light upon exposure to stimulating rays When a certain phosphor is exposed to a radiation, the phosphor stores a part of the energy of the radiation. When the phosphor exposed to the radiation is subsequently exposed to stimulating rays such as visible light, the phosphor emits light in proportion to the stored energy of the radiation. The phosphor exhibiting such a property is referred to as a "stimulable phosphor".
In the radiation image recording and reproducing system employing such a stimulable phosphor, the radiation image information of an object such as a human body is stored in a sheet having a layer of stimulable phosphor, and then the stimulable phosphor sheet is scanned with stimulating rays such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is then photoelectrically detected to produce an image information signal that is electrically processed for generating image information which is recorded as a visible image on a recording medium such as a photosensitive material or displayed as a visible image on a CRT or the like.
One arrangement for reading recorded image information from a stimulable phosphor sheet in such a system employs a light deflector such a galvanometer mirror for deflecting a light beam such as a laser beam. If the light deflector has an accuracy error, then the speed at which the stimulable phosphor sheet is scanned with the light beam is varied, making it impossible to obtain accurate image information from the stimulable phosphor sheet. More specifically, if the scanning speed of the light beam is not constant, the time in which the light beam is applied to the stimulable phosphor is varied, and no accurate image information can be obtained.